IDENTIFICATION OF BRAIN-METABOLITES BY MAGNETIC-RESONANCE SPECTROSCOPY IN MND ALS/

Magnetic resonance spectroscopy (MRS) has provided a novel means of st udying the brain biochemistry of motor neurone disease/amyotrophic lat eral sclerosis (MND/ALS) patients in vivo in situ. Previous studies ha ve demonstrated changes in the ratios of areas under specific spectral peaks in MND/ALS patients (Jones et al., 1995). However, the signific ance of such findings cannot be fully elucidated without first ascerta ining the biochemical identity of each peak. Each peak in a MRS spectr um corresponds to the resonance of specific protons in a particular ch emical environment. Many biochemicals contain similar protons in simil ar environments so it is possible that a single spectral peak could re present protons from more than one biochemical. In this study of major brain MRS peaks we have demonstrated that peaks are potentially compo sed of a number of protons from different chemicals, For example, the peak at chemical shift 2.01 ppm, conventionally recognised as the neur otransmitter N-acetyl aspartate, may actually be a result of the proto ns of the N-acetyl moiety (Frahm et al., 1991). We have consequently s hown that other N-acetylated compounds such as N-acetyl glutamate are also capable of producing a peak here, whereas their non-acetylated de rivatives are not. We have also shown GABA is capable of producing a p eak at chemical shift 3.00 ppm, a peak which is generally assigned to creatine/phosphocreatine. These findings have important implications i n the identification of spectral peaks in MRS studies and in the inter pretation of spectral differences between MND patients and controls.